The connector typically includes a pin member and a box member. The pin member may have a threaded outer surface and the box member may have a corresponding threaded inner surface allowing the pin member and box member to be connected, forming a threaded connection. Connectors of this type are generally used in oilfield applications, for instance to connect sections of wellbore casing or production tubing. Often, connectors for oilfield applications are required to provide liquid-tight and/or gas-tight sealing and to have a strength at least approximately equal to the body strength of the pipe sections joined by the connectors.
Recently, expandable tubular technology has become commercially available. Herein, expandable pipes are radially expanded downhole. The outer diameter of the pipes are increased, for instance, in the range of about 10% to 25%. Many wells have already been cased or lined using expandable tubulars. Expandable tubulars—such as expandable casings or liners—are typically also comprised of pipe sections which are interconnected using threaded connections. Each pipe section typically has a length in the order of 10 metres.
An API (American Petroleum Institute) threaded connector is a commonly used type of connector which performs relatively well at relatively low cost. The API connector however may not always provide reliable gas-tight sealing. In view thereof the API threaded connectors are primarily used for liquid service applications, while more expensive connections, so-called premium connectors, are typically used for applications where gas-tight sealing is required, for instance in production casing or production tubing of gas wells. Most conventional premium connectors have specially designed threads, and rely on metal-to-metal interference for leak tight sealing.
In order to improve the gas sealability of API threaded connectors it has been proposed to apply a soft metal plating to the threaded surfaces. Examples of such plating material include zinc phosphate, zinc and tin. U.S. Pat. No. 5,212,885 discloses a threaded connector wherein the threaded section of each pin member is marked with a band, and wherein the threaded surface of the box member is plated with tin. A thread lubricant is applied to the threads of the box member, and the pin and box members are screwed together until the face of the box member overlaps the band. The connection is considered acceptable if the face of the box member is properly positioned over the band on the pin member, and if the make-up torque is within predetermined limits. Proper make-up of the connector of U.S. Pat. No. 5,212,885 may be difficult or impossible if the coating layer is too thick, and unallowable deformation of the pin member or the box member may occur. The make-up torque can become excessive and poor thread engagement can occur which negatively impacts performance of the connector. This connector is unsuitable to be expanded and will probably leak after expansion.
To ensure leak tightness after expansion, expandable pipes typically comprise premium connectors. Still, the connectors often are the weakest link in the expansion process mainly due to the complicated stress distribution along the thread profile during expansion. Severe plastic deformation during the expansion process may totally destroy the sealing mechanism of the connector, including the metal-to-metal seal of a premium connector. Hence the need arises to develop alternative connections which can survive high expansion ratios (up to 30% or even 35% in some cases) and be leak tight (liquid tight and preferably gas tight) after expansion.
U.S. Pat. No. 6,417,147 discloses a combination of a mechanical and metallurgical connection for joining members such as conduits wherein amorphous diffusion bonding material is placed at mating or abutting surfaces in the mechanical joint. The bonding material is compressed under pressure and heat is applied to cause the bonding material to diffuse into the mechanical connection.
U.S. Pat. No. 6,860,420 discloses a method of interconnecting a pair of metal oilfield tubulars having complementary tapered edges. The tapered edge of at least one of the tubulars at the common contact surface thereof is provided with a thin layer of a metal having a melting temperature lower than the melting temperature of the tubular. The tubulars are interconnected, and heat is applied to the thin layer of metal to melt the thin layer of metal, followed by cooling the tapered edges wherein a metallurgical bond is created between the tubulars. Subsequently the tubular are radially expanded in the wellbore.
As resources become ever scarcer, recently wells have been drilled in ever more challenging environments. For instance, wellbores have been drilled in deep water and/or in high pressure hydrocarbon reservoirs. Deep water herein may indicate more than 1 km water depth. High pressure may for instance indicate reservoirs at a pressure of more than 100 bar. However, pressures up to 400 bar or more are not uncommon, in exceptional cases even exceeding 1200 bar. To render matters worse, the hydrocarbons in the reservoirs may comprise contaminations, typically including corrosive and/or toxic gasses such as H2S or CO2. The expanded tubing, including the expanded connections, is expected to contain said gases up to the maximum pressure to which the tubing in a worst case may be exposed.
Based on a challenging drilling scenario, for instance in the Gulf of Mexico, it was also established through computer modelling that the connections should preferably be able to survive a drilling torque. Rotating the tubing may be required to introduce the tubing into the well beyond a threshold depth. For example, a pipe having an outer diameter (OD) of 5.5 inch may be required to withstand a torque of about 7000 ft-lbs (about 9.5 kNm) or more. Rotating the pipe may be required to be able to introduce the pipe more than about 3,000 feet into the wellbore.
There is currently no connection available in the market that can survive expansion and remain leak tight after expanding the outer diameter about 20% or more. However, the challenging drilling scenarios presented above have created a need for connections which can be leak-tight, and preferably gas-tight, after expansion.